Process and apparatus for producing powder particles by atomization of a feed material in the form of an elongated member

Abstract

The present disclosure relates to a process and an apparatus for producing powder particles by atomization of a feed material in the form of an elongated member such as a wire, a rod or a filled tube. The feed material is introduced in a plasma torch. A forward portion of the feed material is moved from the plasma torch into an atomization nozzle of the plasma torch. A forward end of the feed material is surface melted by exposure to one or more plasma jets formed in the atomization nozzle. The one or more plasma jets being includes an annular plasma jet, a plurality of converging plasma jets, or a combination of an annular plasma jet with a plurality of converging plasma jets. Powder particles obtained using the process and apparatus are also described.

What is claimed is: 
     
       1. An apparatus for producing powder particles by atomization of a feed material in the form of an elongated member, comprising an inductively coupled plasma torch with a longitudinal axis and including:
 a coaxial injection probe at a first end of the inductively coupled plasma torch and comprising an elongated conduit which extends through at least an upstream portion of a coaxial plasma confinement tube of the plasma torch for introducing the elongated member of feed material axially into the plasma torch; and 
 an atomization nozzle at a second end of the plasma torch opposite the first end, wherein the atomization nozzle comprises an aperture coaxial with the longitudinal axis for receiving the elongated member of feed material from the coaxial injection probe, and wherein the atomization nozzle is configured for producing, using plasma from the inductively coupled plasma torch, at least one feed material atomizing plasma jet for surface melting and atomizing feed material of a forward end of the elongated member by exposure to the at least one feed material atomizing plasma jet. 
 
     
     
       2. The apparatus of  claim 1 , comprising a preheating zone for preheating a forward portion of the elongated member of feed material, using plasma produced in the inductively coupled plasma torch, the preheating zone being positioned within the plasma torch between the coaxial injection probe and the atomization nozzle. 
     
     
       3. The apparatus of  claim 2 , wherein the forward portion of the elongated member of feed material is preheated by direct contact with plasma in the preheating zone. 
     
     
       4. The apparatus of  claim 2 , comprising a radiation tube in the preheating zone, wherein the forward portion of the elongated member of feed material is preheated through the radiation tube heated by direct contact with plasma in the preheating zone. 
     
     
       5. The apparatus of  claim 1 , comprising a cooling chamber downstream of the atomization nozzle and on which the inductively coupled plasma torch is mounted coaxially with an axis of the cooling chamber. 
     
     
       6. The apparatus of  claim 5 , wherein the forward end of the elongated member of feed material exits the plasma torch through the coaxial aperture into the cooling chamber in which the forward end of the elongated member of feed material is exposed to a plurality of plasma jets spaced apart around the longitudinal axis and converging toward the longitudinal axis. 
     
     
       7. The apparatus of  claim 5 , wherein the cooling chamber is sized and configured to allow in-flight freezing of droplets formed by atomization of the feed material using the atomization nozzle. 
     
     
       8. The apparatus of  claim 1 , comprising a mechanism for supplying the elongated member of feed material to the injection probe, the mechanism being adapted to control a feed rate of the elongated member. 
     
     
       9. The apparatus of  claim 8 , wherein the mechanism is also adapted to straighten the elongated member within at least one plane. 
     
     
       10. The apparatus of  claim 1 , wherein the inductively coupled plasma torch generates plasma from a gas selected from argon, helium, hydrogen, oxygen, nitrogen and a combination thereof. 
     
     
       11. The apparatus of  claim 1 , wherein the atomization nozzle comprises a plurality of radial apertures spaced apart around the longitudinal axis and in which plasma from the inductively coupled plasma torch flows to produce a plurality of plasma jets converging toward the longitudinal axis. 
     
     
       12. The apparatus of  claim 11 , wherein the coaxial aperture of the atomization nozzle is sized and configured to closely match a cross-section of the elongated member of feed material so that the coaxial aperture is substantially closed by insertion of a forward portion of the elongated member of feed material, building up a pressure of the plasma in the plasma torch and causing the production of the plurality of converging plasma jets. 
     
     
       13. The apparatus of  claim 1 , wherein the coaxial aperture of the atomization nozzle is sized and configured to leave a gap between the coaxial aperture and the elongated member of feed material so that an annular plasma jet is formed within the coaxial aperture and around the forward end of the elongated member of feed material. 
     
     
       14. The apparatus of  claim 1 , wherein:
 the atomization nozzle comprises an internal face tapering off toward the coaxial aperture; and 
 the coaxial aperture of the atomization nozzle is sized and configured to closely match a cross-section of the elongated member of feed material so that moving the elongated member of feed material toward the coaxial aperture builds up a pressure of the plasma in the inductively coupled plasma torch and causes the production of an annular plasma jet. 
 
     
     
       15. The apparatus of  claim 1 , comprising:
 an input port for receiving a sheath gas; and 
 an annular output port positioned downstream of the atomization nozzle for injecting the sheath gas surrounding atomized material from the inductively coupled plasma torch. 
 
     
     
       16. The apparatus of  claim 15 , wherein the inductively coupled plasma torch generates plasma from a plasma gas, and wherein the sheath gas and the plasma gas are a same gas. 
     
     
       17. The apparatus of  claim 15 , wherein the inductively coupled plasma torch generates plasma from a plasma gas, and wherein the sheath gas and the plasma gas are different gases. 
     
     
       18. The apparatus of  claim 1 , wherein the at least one feed material atomizing plasma jet is a high velocity plasma jet, and wherein the high velocity is selected from the group consisting of sonic and supersonic velocities. 
     
     
       19. The apparatus of  claim 1 , wherein the elongated member is selected from the group consisting of a wire, a rod and a filled tube. 
     
     
       20. The apparatus of  claim 1 , wherein the apparatus is configured to change a chemical composition of atomized material obtained by surface melting and atomizing of the feed material through a reaction between different components premixed into the feed material, or as a result of a chemical reaction between a plasma gas or a sheath gas and the atomized material.